Improvements in the operation of ink-jet printers are constantly sought. Among such needed improvements are a means of ensuring that an ink-jet cartridge is securely locked in place in a cartridge carrier, that the cartridge is registered in a given, fixed, repeatable position each time, that the cartridge be spaced from the printing medium a minimum, fixed distance, that the carriage include means for maintaining this fixed distance, and that protected interconnect means be provided to connect the printhead mechanism on the cartridge with a microprocessor for controlling the pattern of ink drop ejection.